In some cases, if the crater formed by a mine explosion was some distance from the British front line, no infantry action would follow. If, however, a mine was blown under a British trench, it was usually accompanied by an enemy raid, which was planned to enter our trenches during the confusion caused by the mine and surprise the surviving garrison. If, on the other hand, it was blown in No Man's Land close to the British front line, it was necessary at all costs to prevent the enemy from occupying it. Thus in the two last cases heavy infantry fighting often occurred. In the latter case, the object of these actions was to prevent the enemy from establishing himself on the crater. If he did so the position was serious, for the crater became a permanent menace to the security of our lines. Where the ground might have been flat, a large hollow mound had now arisen. If the enemy established himself on the British side of the mound (_i.e._, the near lip, as it was called), he might construct sniping-posts which would dominate the trenches. Should he only establish himself on the far lip, he still was able, by working around the lip of the crater towards the flank, to shoot down into our trenches in enfilade. It was suggested that the Germans, by some peculiar method of tamping (_i.e._, packing the explosive in the chamber), used to blow his craters with the far lip higher than the near lip. Thus, if he only established himself on the far lip, the near lip, being lower, did not obscure his view to the front; conversely the view from the near lip, if occupied by the British, was obscured to the front by the higher far lip. Whether his craters were formed in this manner from accident (_i.e._, the lie of the ground) or from design is not clear. The fact remained that an examination of many craters in the Neuville St Vaast area proved this to be the case. These crater fights often developed into considerable minor operations involving many casualties. They almost always took place in the dark, and were an unpleasant ordeal for all concerned. The crater, still smoking from its base like a miniature volcano; the stench of the fumes; the whiteness of the freshly-turned chalk standing out in the darkness, produced a setting which intensified the normal horrors of battle. When the German blew a mine he, of course, knew the hour and the place at which the explosion would occur. He knew also from the depth of his gallery and from the amount of explosive used how close to the spot his assaulting troops might assemble without fear from the falling débris. He was also able to assemble dumps of loophole plates, prepared and portable obstacles, bombs, &c., close to the scene of operations. The troops might or might not have been warned that a mine was to be expected in a certain area.